Reforestation of coniferous forests after logging or forest fires is generally accomplished by tree planting by hand. Tree planters, on foot and carrying a supply of tree seedlings, form holes in the soil using a tool called a mattock and insert a tree seedling into the hole, and the soil is pressed around the roots of the seedling by the planter. Due to the nature of coniferous forests, such re-planting is often carried out on rugged terrain, in difficult soil conditions. Also, such forests are typically in a northern climate with a short growing season. There is therefore a short window during which the re-planting of seedlings has the maximum chance for success, when the soil is sufficiently warm and moist with a long enough season remaining for the roots of the seedling to develop enough for survival.
Previously, tree seedlings were grown for up to three years in a nursery and then transplanted with bare roots. The disadvantages of such “bare root” planting of tree seedlings have been outlined in the present inventor's prior U.S. Pat. No. 3,722,139. Bare root replanting of tree seedlings has a high failure rate, since the soil into which the seedling is planted may have been overly harsh, cold or dry and the seedling roots may not have time to develop adequately in a short growing season. Consequently a method of growing seedlings in a soil plug called “styroblock plugs” has been developed. The soil plug can be planted using a dibble rather than a mattock. According to the current method, styrofoam trays or blocks having an array of cylindrical cavities are used. The cavities are filled with a loose growing soil mixture consisting of peat moss, sawdust and additives covered with loose sand. Generally two tree seeds are placed in each cavity. The trays are then placed in a greenhouse for the seed to germinate in warmth and light. After about 7 months the roots of the seedling have sufficiently developed to hold the growing medium together, forming a plug. At that point the seedlings are ejected from the styrofoam blocks and wrapped and packed for shipping or storage. In this way the roots of the seedling when planted are assured of a moist growing medium.
There remain difficulties with this present method, however. Roots of seedlings which have sufficiently developed in the cavity to retain the growing medium are not ideally configured for replanting as they form a ball which is unstable when replanted, and the growing seedling may be blown over in the wind. This is particularly a problem with certain species such as lodgepole pine. It is preferable to have the seedling roots develop naturally by penetrating into the upper layers of humus. Further, a long growing time is required to allow the seedling roots to develop according to this method, typically a minimum 7 months. Generally the seedlings will be planted in Jan. and shipped in Jul. However Jun. is often a preferable month for planting in order to minimize failures. Consequently there is a need for a method of forming a seedling plug which permits transplanting at an earlier stage of development of the seedling root system.